Same problem here, I sent a $600 card back at the start of March via registered express with insurance and it is still sitting at the airport. The buyer has not been in contact but they put in a claim for a refund and was successful even though the tracking details clearly state it is still in transit. I escalated the case through Australia Post and they replied saying that the card is in safe holding at the airport and ready to be delivered as soon as the borders open up.
Meanwhile I was forced to refund the buyer on Friday, I appealed the decision and it was denied instantly because the card hasn't been delivered since early March even thought he tracking clearly shows that it is still in transit. The buyer from Taiwan will most likely receive the card providing the mail is not redirected back and get to keep their money.
I spent a good hour eBay chat this morning and was told there is nothing i can do until the tracking number shows that it has been delivered.
I personally think that the payment should remain on hold until the tracking shows it is delivered or lost but as usual eBay always protect the buyers regardless of what evidence you throw on the table.